1. Field of the Invention
The present invention relates to apparatuses, methods, and programs for processing images, and in particular, relates to apparatuses, methods, and programs for processing images suitable for enhancing the contrast of images appearing on displays having a fixed luminance dynamic range from a white level to a black level, for example, liquid crystal displays. The white level is a luminance level when white is displayed, and the black level is a luminance level when black is displayed.
2. Description of the Related Art
Direct current (DC) transmission rate correction is known as a method for enhancing contrast of the image when an overall image of, for example, television is bright. In DC transmission rate correction, luminance signals, out of input image signals (referred to as input signals hereinafter), are averaged. Then, a predetermined value depending on this average value (referred to as average luminance hereinafter) is uniformly subtracted from the luminance of each pixel. This method is disclosed in, for example, Japanese Unexamined Patent Application Publication No. 2003-131623, especially paragraph 15 and FIG. 4.
In DC transmission rate correction, for example, input luminance signals having luminance levels shown in FIG. 1 are corrected and output as output luminance signals having luminance levels shown in FIG. 2. In this correction, the luminance levels of the input luminance signals are uniformly reduced regardless of the individual levels, as shown in FIG. 2. In FIGS. 1 and 2, the abscissa indicates time t, and the ordinate indicates the luminance level. A white level and a black level are indicated on the ordinate.
Luminance signals having luminance levels that are relatively low but higher than the black level in FIG. 1 are displayed as black by correction, as shown in FIG. 2. Thus, the darkness in an image is emphasized.
The output luminance signals in FIG. 2 shows that high luminance levels for displaying white in FIG. 1 are also reduced in DC transmission rate correction. However, as shown in FIG. 3, in a display having a variable luminance dynamic range from a white level to a black level, such as a cathode ray tube (CRT), the white level can be adjusted independently of DC transmission rate correction. Thus, intended white can be displayed from luminance signals for white.